The present invention relates to devices for delivering, injecting, dispensing, infusing or administering substances, and to methods of making and using such devices. More particularly, it relates to an injection device comprising a dose metering mechanism for selecting and/or administering doses of an injectable product. More particularly, it relates to a dose metering mechanism comprising a latching control device for controlling the latching action of catch elements of a feed sleeve and a guide piece in the teeth of a toothed rack to enable a priming dose and another dose to be dispensed, wherein the priming and another doses may be different, set or selected easily and in a user-friendly manner, and dispensed from the injection device.
When using injection devices, for example injection pens, with which a substance such as a medicinal substance or a medicament, e.g., insulin, hormones, etc., can be administered in doses, it is customarily first necessary to set what is referred to as a priming quantity or dose which has to be dispensed during priming. Generally, the purpose of priming is to vent an injection cannula associated with the injection device, with a view to freeing the cannula of any residual substances and/or air. Generally, this is done by ejecting a specific small quantity of the product to be injected from the cannula or needle of the injection device without actually administering an injection. The dose or amount of the substance to be injected, which is usually bigger than the priming amount, can then be set and/or injected.
In a known injection device, teeth are provided on a toothed rack at a constant distance apart, in which snappers or engagement structures of a feed sleeve and a guide sleeve can engage. The teeth of the toothed rack can be pushed past the guide sleeve to dispense the substance from the injection device, and the snapper of the guide sleeve latching in the teeth causes an additional clicking sound during the dispensing operation, which can unsettle the user during the injection.